Re: [Ext2-devel] [RFC] [PATCH] Reducing average ext2 fsck time through fs-wide dirty bit]

[Andreas Dilger <adilger@clusterfs.com>]

On Mar 24, 2006  15:01 -0500, Theodore Ts'o wrote:
> On Fri, Mar 24, 2006 at 12:28:02PM -0700, Andreas Dilger wrote:
> > The good news, is that fixing the "ext3 clearing indirect blocks" problem
> > not only allows undelete to work again, but also improves truncate
> > performance because (a) we only modify 1/32 of the blocks we would in the
> > old case (we don't need to modify any {d,t,}indirect blocks), (b) we do
> > indirect block walking in forward direction, and could submit {d,}indirect
> > block requests in a batch instead of one-at-a-time.
> 
> the thing that scares me about this is that this means we now
> have to maintain *two* horribly complicated pieces of code for which
> it will be very easy for bugs to creep in.  

That is why I propose keeping the majority of this code common (the tree
walking part), and only fix the bottom layer which adds the {d,t,}indirect
blocks into the transaction and zeroes them out, and the top layer, which
decides which path to take.

> This would be a prime candidate for trying to add the same sort of
> userspace test framework which Rusty and company did for netfilter, so
> we can try to test for race conditions, corner cases, etc.

Are you saying to make a filesystem test harness in userspace, or to
add hooks into the kernel to trigger specific cases in the running
kernel?

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.